Spring/SpringBoot/SpringCloud Mybatis 执行流程

在后续分析Mybatis 流程中代码的可能会用到IDEA debug 技巧：

1. 条件断点
   代码断点，右键 勾选弹窗 Condition ： 写入表达式

2. 回到上一步：
   
   
   

3. Java动态代理实现 InvocationHandler接口：

package com.lvyuanj.core.test;

import com.lvyuanj.core.model.User;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface UserTestMapper {

	@Select("select * from t_user")
	public List<User> query();
}

package com.lvyuanj.core.test;

import org.apache.ibatis.annotations.Select;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyInvocationHandler implements InvocationHandler {

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		System.out.println("query db:"+ method.getAnnotation(Select.class).value()[0]);
		return null;
	}

}

package com.lvyuanj.core.test;

import java.lang.reflect.Proxy;

public class MyQueryTest {

	public static void main(String[] args) {
		Class[] clazz = {UserTestMapper.class};

		UserTestMapper userTestMapper = (UserTestMapper) Proxy.newProxyInstance(MyQueryTest.class.getClassLoader(), clazz, new MyInvocationHandler());
		userTestMapper.query();
	}
}

mybatis 核心FactoryBean

MapperScannerRegistrar
实现了ImportBeanDefinitionRegistrar 接口。 可以自动注入

MapperScannerConfigurer 实现 BeanDefinitionRegistryPostProcessor这个类
postProcessBeanDefinitionRegistry（）中扫描注入mapper

MapperFactoryBean 实现了FactoryBean 也继承了SqlSessionDaoSupport 类；

Spring 管理MapperFactoryBean 的时候设置属性的时候初始化SqlSessionTemplate

public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
    if (this.sqlSessionTemplate == null || sqlSessionFactory != this.sqlSessionTemplate.getSqlSessionFactory()) {
      this.sqlSessionTemplate = createSqlSessionTemplate(sqlSessionFactory);
    }
  }

需要的SqlSessionFactory 在AppConfig中定义，由于SqlSessionFactoryBean实现FactoryBean接口类，factoryBean.getObject(); 获取到真实的对象SqlSessionFactory

在创建对象的时候时候进行afterPropertiesSet(); 对象

 public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

@Bean
public SqlSessionFactory sqlSessionFactory() throws Exception {
    SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
    factoryBean.setDataSource(dataSource());
    return factoryBean.getObject();
}

当开发者调用userMapper.selectAll() 方法的时候，由于userMapper是MapperFactoryBean 工厂bean创建的Bean的时候调用的是MapperFactoryBean.getObject(); 最终调用org.apache.ibatis.binding.MapperRegistry#getMapper(Class type, SqlSession sqlSession)
方法中调用 mapperProxyFactory.newInstance(sqlSession)

@Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

SqlSessionTemplate 是SqlSession 的实现类，

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
    notNull(executorType, "Property 'executorType' is required");

    this.sqlSessionFactory = sqlSessionFactory;
    this.executorType = executorType;
    this.exceptionTranslator = exceptionTranslator;
    this.sqlSessionProxy = (SqlSession) newProxyInstance(SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class }, new SqlSessionInterceptor());
  }

@Override
  public <T> T selectOne(String statement, Object parameter) {
    return this.sqlSessionProxy.selectOne(statement, parameter);
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public <K, V> Map<K, V> selectMap(String statement, String mapKey) {
    return this.sqlSessionProxy.selectMap(statement, mapKey);
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) {
    return this.sqlSessionProxy.selectMap(statement, parameter, mapKey);
  }
  
  ......

代理类

private class SqlSessionInterceptor implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      SqlSession sqlSession = getSqlSession(SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);
        
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {  //是否启用事务管理，没有事务管理mybatis自己管理
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
        Throwable unwrapped = unwrapThrowable(t);
        if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
          // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          sqlSession = null;
          Throwable translated = SqlSessionTemplate.this.exceptionTranslator
              .translateExceptionIfPossible((PersistenceException) unwrapped);
          if (translated != null) {
            unwrapped = translated;
          }
        }
        throw unwrapped;
      } finally {
        if (sqlSession != null) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }

开始涉及MyBatis SqlSession部分的一些机制，关于MyBatis sqlSession的一点整理，SqlSession主要是MyBatis定义的用于进行持久化操作的对象，对connection进行了包装。在上面Spring Transaction的机制中，我们获取到了connection，之后会首先调用SqlSessionUtils里面的getSession方法，判断当前的sqlSessionHolder以及是否存在事务锁定。

public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
    notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);

    SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

    SqlSession session = sessionHolder(executorType, holder);
    if (session != null) {
      return session;
    }

    LOGGER.debug(() -> "Creating a new SqlSession");
    session = sessionFactory.openSession(executorType);

    registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);

    return session;
  }

sessionFactory.openSession(executorType); sessionFactory上文中在sqlSessionFactoryBean 实现InitializingBean接口初始化的时候afterPropertiesSet() 方法被调用
this.sqlSessionFactory = buildSqlSessionFactory(); 执行是new DefaultSqlSessionFactory()对象。

  @Override
  public SqlSession openSession(ExecutorType execType) {
    return openSessionFromDataSource(execType, null, false);
  }
  
  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment); 获取事务工厂类，第一次的时候new ManagedTransactionFactory();
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit); 创建一个事务对象
final Executor executor = configuration.newExecutor(tx, execType);

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      executor = new ReuseExecutor(this, transaction);
    } else {
      executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

UserMapper 初始化到调用链流程图